The present invention relates to a pattern formation method in which a resist film made from a chemically amplified resist material is selectively irradiated with extreme UV of a wavelength of a 1 nm through 30 nm band so as to form a resist pattern from an unexposed portion of the resist film.
In processes for semiconductor integrated circuit devices, lithography technique is desired to be further developed in accordance with increase of the degree of integration and downsizing of semiconductor integrated circuits.
As exposing light employed in the lithography technique, a mercury lamp, KrF excimer laser (of a wavelength of a 248 nm band), ArF excimer laser (of a wavelength of a 193 nm band) or the like is currently used. For the generation of 0.1 μm or less, and particularly of 0.05 μm or less, extreme UV of a wavelength (of a 1 nm through 30 nm band) shorter than that of the ArF excimer laser is now being examined to be used.
In the lithography technique using extreme UV as the exposing light, a chemically amplified resist material with high resolution and high sensitivity is preferably used.
Therefore, in the lithography technique using extreme UV, a chemically amplified resist material suitable for the ArF excimer laser lasing at a wavelength close to that of extreme UV is now being examined for use.
Now, a pattern formation method using a chemically amplified resist material suitable for the ArF excimer laser will be described with reference to FIGS. 4A through 4D.
First, a chemically amplified resist material having the following composition is prepared:
Base polymer: poly((2-methyl-2-adamantyl acrylate)-(methyl methacrylate)-(methacrylic acid)) (wherein 2-methyl-2-adamantyl acrylate:methyl methacrylate:methacrylic acid=70 mol %:20 mol %:10 mol %) . . . 2 g
Acid generator: triphenylsulfonium triflate . . . 0.4 g
Solvent: propylene glycol monomethyl ether acetate . . . 20 g
Next, as shown in FIG. 4A, the chemically amplified resist material having the aforementioned composition is applied on a semiconductor substrate 1 so as to form a resist film 2 with a thickness of 0.2 μm.
Then, as shown in FIG. 4B, the resist film 2 is selectively irradiated for pattern exposure with extreme UV 4 (of a wavelength of a 13.5 nm band) through a reflection mask (not shown) having a desired mask pattern. After the pattern exposure, as shown in FIG. 4C, the resist film 2 is subjected to post-exposure bake (PEB) 5 with a hot plate at a temperature of 100° C. for 60 seconds.
In this manner, an exposed portion 2a of the resist film 2 becomes soluble in an alkaline developer owing to a function of an acid generated from the acid generator while an unexposed portion 2b of the resist film 2 remains insoluble in an alkaline developer because no acid is generated from the acid generator therein.
Next, the resist film 2 is developed with an alkaline developer, such as a 2.38 wt % tetramethylammonium hydroxide developer, so as to form a resist pattern 6 with a line width of 0.07 μm from the unexposed portion 2b of the resist film 2 as shown in FIG. 4D.
However, since large roughness 6 has been caused on the surface of the resist pattern 6, variation in the line width of the resist pattern 6 is disadvantageously large. When the line width of the resist pattern 6 is measured, a difference between the maximum width and the minimum width is as large as approximately 20 nm.
As the design rule of semiconductor integrated circuit devices is reduced, the variation in the sizes of a resist pattern, such as the line width and the dimension of an opening, causes influence more difficult to ignore. Specifically, when a conducting film or an insulating film is etched by using a resist pattern with such size variation, the line width or the dimension of openings can be varied in the resultant pattern, which disadvantageously lowers the accuracy of a semiconductor integrated circuit device.